Signal mixing circuits



Oct. 14, 1952 R. c. .GoERTz 2,514,237

SIGNAL MIXING CIRCUITS Filed Deo. 2s, 194e 2 SHEETS- SHEET 1 r9 T TOR/VE V,

Oct. 14, 1952 R. c. GoERTz SIGNAL MIXING CIRCUITS 2 SHEETS-SHEET 2 Filed Dec. 28, 1946 Patented Oct. 14, 1952 SIGNAL MIXING CIRCUITS Raymond C. Goertz, Hempstead, N. Y., assigner to The Sperry Corporation, av corporation of Delaware.

Application December 28, 1946, Serial'No. 718,966

7 Claims.`

a predetermined'amountV exists between the position of the object driven by the servomotor and the position of the reference device.

It is an object of this invention to provide an electrical circuit for producing an output voltage mainly corresponding toeither the ne or the coarse input, the selection depending upon the extent of disagreement existing between the object driven by the output and the reference device.

Another object resides in providing a mixing and controlling circuit for iine and coarse signal voltages, comprising electronic means having an output controlled by the line signal voltage to the exclusion of the coarse signal voltage under one set of conditions, and having the output controlled by the coarse signal voltage to the exclusion of the fine signal voltage under an*- other set of conditions.

A further object is to provide a mixing circuit includingl high impedances in circuit with both thene and the coarse signal inputs, one of said impedances including electronic means for affording isolation of one input signal in the operating region of the other, and also providing smooth transition from fine to coarse inputvand vice versa, thereinbetween.

More particularly, an object is to provide a mixing circuit including a high impedance in series with the fine signalinput, and an electronic circuit including a diode electron tube, in circuit with the coarse error signal. Said diode serving toblock the coarse error signal from control of the outputv by presenting an innite impedance to said coarse error signal in the operating region of the fine error signal, and said diode presenting a relatively small impedance'to Said coarse error signal in the operating region of said coarse error signal whereby the impedance in circuitwith said fine error signal, being relatively large, effectively blocks said fine error signal in the operating regionfof said-coarse error signal.

- Theinvention also relatesto the novelieatures or principles of the instrumentalities described herein, whether or not such are used for the stated objects. or in the stated fields or combinations.

Other objects and advantages will become apparent from the specification, taken in connection with the accompanying drawings wherein,

Fig. l is a schematic diagram of a servo system embodying a simplied version of the mixing circuit of the instant invention;

Fig. 2 is a graph illustrating the relationship between lne and coarse signals and the output;

nFig. 3 is a graph illustrating an alternative relationship between fine and coarse signals and the output;

Fig. 4 is a schematic diagram showing a complete circuit for a servo system embodying a preferred form of the instant invention.

Referring now to the drawings, Fig. l illustrates the instant invention as embodied in a simplified mixing circuit. In Fig. 1, fine and coarse signals are produced in response to angular displacement of a reference device which, though not shown, may be operatively connected to cause rotation or the shaft l l. Rotatable with the input shaft I I, is a rotor I2, which is energized by an alternating current source I3, thereby inducing in the transmitter I4 an electromagnetic field which will assume a position dependent upon the angular position of the rotor I2. This electromagnetic iield is reproduced in direction in the receiver unit I", located at some position removed from the transmitter unit I4 and connected thereto through leads i5. Rotor Il is arranged to rotate within the iield of the stator of receiver unit I5 and is positioned in an angular sense by the motor i3 in accordance with the position of the load shaft I9 as transmitted through shafts 2i, 22 and 23 and associated gearing.

, As the object of the entire system is to energize the motor I8 to drive the load shaft I9 into positional agreement with the reference device that is operatively associated with the input shaft I I, upon the occurrence of a disagreement between the angular position of the shaft I9 and the angular position of the reference shaft II, a corresponding angular discrepancy or asynchronisxn will be evidenced between the rotor ll which was positioned by the motor It, and the rotor I2 which was positioned by the reference device and the input shaft II. Inasmuch as the angular posi.- tion of rotor I2 is transmitted to the `Vreceiver t6, any disagreement existing between the rotor I'I and the position of the field created by the receiver I6 will serve to create an output signal across the point 24, that is dependent, in amplitude, upon the extent of disagreement existent between the load shaft i9 and the reference shaft Il, and, in phase sense, upon the direction of such disagreement, and this signal is hereinafter referred to as the coarse error signal, or the coarse input signal.

In order to provide greater sensitivity or closer synchronization in the region of small angular disagreements between shaft lo and the reference shaft Il, a nne error signal or nne input signal is produced in a manner well known in the art. The electrical circuit for producing a fine error signal is substantially the same as that for producing the coarse error signal, and in this instance includes the rotor 26, transmitter 2i, transmission lines 28, and a receiver unit 29 including rotor 3l. The fine error signal appears across points 32, 33. As is commonly provided in similar` ne and coarse systems, rotation of rotor Z is responsive to rotation of the input shaft l l, but the gear train 34, to which rotor 2t, is operatively connected, produces a rotation of rotor 26 which is some multiple of the rotation of the input shaft, and the ratio of 36:1 is sornetimes chosen. In order to maintain the angular motion of the rotor 3l in the saine ratio with respect to its driving source, or shaft 23, the gear train is provided.

With the apparatus above described, on the occurrence of an angular discrepancy between the load shaft i9 and the reference or input shaft Il, two error signals will be produced. One or" these error signals will appear as an error input signal between the points 24 and 25 and the other error signal will appear' as an error input signal between the points 32 and 33. Furthermore, masmuch as the A. C. source i3 is provided to enn ergize both of the rotors i2 and 2E, both or" the error input signals will be of the same frequency, but due to the ratio of angular displacement of the fine error signal generator as compared to the coarse error signal generator, the cycle of the envelope of the ne error input signal appearing between points 32 and 33 will bear a ratio of 36:1 (or any other predetermined ratio), to the cycle of the envelope of the coarse error signal appearing between points 24 and 25. Fig. in illustrating this relationship, provides a nrs-t Curve labelled Fine Error Signal, and a second curve labelled Coarse Error Signal, and shows the relationship between the outputs of the signal generators as the outputs vary in accordance with the actual displacement or error. Actually the fine error signal will ordinarily have an amplitude much greater than that shown by the curve of Fig. 2, but in order to provide a system wherein the rise of voltage from the fine error signal is substantially the same as for the coarse, a potentiometer 36 is inserted across the iine input signal. Inasmuch as it is desirable to block the coarse error signal from controlling the servomotor I8 for small values of actual error which may be considered as the operating region of the fine error signal (which, in the case illustrated in Fig. 2, has been selected to be approximately zero to plus or minus two degrees of reference error), a pair of diode electron tubes 31 and 38 are provided in circuit with the coarse error input. When non-conducting, diodes oier substantially innite impedance, but when conduction takes place, the impedance drops to the order of a few hundred ohms. Preferably, each of the diodes is biased from some suitable voltage source such, for example. as from the batteries 39 and 4I of preferably equal voltages, in a non-conduct- 4 ing direction. The balancing resistors 42 and 43, of relatively low impedance value, and the condenser 44 serve to assist in providing full phase operation across the diodes 31 and 38, completing the blocking circuit for the coarse signal input.

Resistor 45 of relatively high impedance value (for example, it may be in the order of ten times as great as resistor 42 and 43) is also much higher than the impedance of the diode when conducting, and is connected in series with the fine error signal. The resistor 45 is not of so great a value as to affect the transmission of the ne error signal under the condition presented when the coarse error signal is blocked by the diodes 3'! and 38, but due to its relatively large size as compared to the resistance in the coarse error signal circuit, when the coarse error signal overcomes the bias due to sources 3B and 4l, then resistor 45 serves to virtually block the fine error signal from effecting the operation of the control grid 46 of tube 4'i which, as will presently be disclosed, in turn controls the operation of the servomotor I8.

From the foregoing, it may be seen that each of the grids 4S and 4E of tubes 4l and 48 connected through grid resistors 5I and 52 are at the same D. C. level, with reference to ground, that level being dependent upon the value of the D. C. source 39. However, grid 46 alone receives the A. C. signals, and the voltage at point A controls the grid 4S and thereby, the space discharge path of the tube 4l. Lines 53 and 54 connect the output from tubes 47 and 48 to an ordinary phase sensitive amplifier 5o which in turn controls the rotation of the motors I8 in a manner well known in the art.

The graph of Fig. 2 illustrates the type of output produced by the instant mixing circuit, particularly showing the transition of control from iine to coarse error signal when the bias on the diodes has been overcome. The solid line represents the signal that would appear at point A of the schematic of Fig. l. The slight difference between the graph of the coarse error signal, and the graph of the coarse voltage on the grid (or point A) may be attributed to the total small impedance drop .including that across the diodes 38 and 3l when conducting.

Fig. 3 illustrates the relative signal values when the rate of increase of the nne error signal has been adjusted, by potentiometer 36, to a value more nearly corresponding to the rate of increase of the coarse error signal, for that region, to assist in producing a smooth transition from line to coarse at the point where the diode bias, which up to this point has served t0 block the coarse, is overcome.

While under certain conditions it may be desirable to have a very smooth transition from ne to coarse error signal, in certain applications it may be more desirable to extend the region of ne error signal operation at the sacrifice of maintaining a smooth curve at the transition point. In any event, if the saturation point of the amplifier is reached while the output is still responsive to the ne error signal, the transition from fine to coarse error signal at the point at which the impedance due to the diodes is overcome by the coarse signal, will also be smooth, regardless of the rate of increase of the fine or the coarse error signal.

Fig. 4 illustrates a complete circuit embodying the general concepts set forth in the simplified version illustrated in connection with Fig. l. In Fig. 4, a. line and coarse error signal may be amaze? evolved with 'equipment similar-to :that hereinbefore described in detail for obtainingv nel yand coarse signalsand is indicated generally as |`0|. In the instant embodimentthe'servomotor |02 is provided: to stabilize the platforml |03, supporting a scanner device |04, either in roll or pitch, in accordance with a reference such asv a gyro vertical (not shown) which operates the rotors |05 and |06 of the ne and coarse system |0|. A gear reduction mechanism |01 is` provided for interconnecting the servomotor |02 with the platform |03, and includes a gear train for maintaining a predetermined ratio, such as 36:1, for the receiver rotors |08 and |09 of the fine and coarse system Thus, ifa discrepancy occurs between the angular position of rthe rotors |08 and or |09 and |06, .a fine. error signal will appear acrossy inputy points 1| and I2, and a coarse. error signal will yappear across input points ||3 and |,|'4.

As in the case. involving the,.simplied sche.- matic :of Fig. l, a pair of diodes, herein appearing'as the duo-diodey I |5 is provided for blocking the coarsey input signal under the condition of.

shown; forismoothing .the rectified voltage. The:

voltage divider :includes: resistors ||9,. |22 and |23, and resistors 2| and` |24 serve to provide equall biases in a .non-.conducting direction on both halves of the diode ||5. Thus, the coarse error voltage is blocked byv the high impedance provided by the diode ||5 until such time as the bias obtained through the voltage-dropping. cir-- cuit is overcome by the coarse error signal.

In circuitA with the ilne error signal is a pair of voltage-dropping resistors |25 and |26 connected with a4 relatively high impedance such as resistory |21. Thehigh impedance of resistor |21 has' no material effect during the time when the coarse error signal isblocked, but once the-.coarse error signal becomes large enough to overcome the bias, the impedance in circuit with the coarse error signal is so small as compared to the high impedance offered by resistor |21, that the operation of the grid |28 is controlled by the coarse error signal in a manner similar to the operation described in connection with the simplified schematic of Fig. l. The other grid |3| of the tube |29 is maintained at a constant D. C. level above ground, being tied into the voltage-dropping circuit through line |32 to the high side of resistor |23.

The output of tube |29, being governed eiectively either by the iine or the coarse error signal in the manner described, will then appear across the resistor |33, connected across the primary of the coupling transformer |34. The secondary of the coupling transformer is then fed to a full wave, phase sensitive rectier, including tubes |35 and |40, and tubes |36 and |31 in a circuit arrangement well known to the art, and rate-taking circuits |38, for producing a signal component in the output of the rectiiier proportional to the rate of change of the error signal input, is also included. The output from this rectier appears across points |39 and |4| as a unidirectional voltage, varying in magnitude with the amplitude of the input signal and of a polarity dependent upon the phase sense of the input signal. The rate circuits modify the foregoing by producing a rate component in the rectier outputs;

pliiier |43 being connected differentially to the control field |44 of the constantl armaturey current motor |02.

Since many changes could be lmade in the above construction and manyr apparentlyf widelyl different embodiments ofi thisr invention couldy be made without departure .from thescopefthereof, it is. intended that all matter contained in.

be mixed, means including a relatively high yim-A pedance for connecting one vof said inputs, to said control electrode, means including a pair :of diode electron tubes and a source of vbias potential connected therewith, said tubeshaving space discharge paths connected for full phase operation of said applied voltagefor blocking the voltage supplied thereto below a predetermined value but passing voltages in excess thereof to its out-V put, and means for connecting the output of said last mentioned means to said control electrode between it and said high impedance, the. impedance offered by said pair of. diodes being `infinite under blocking condition butIv low as com-v pared to the value of said impedancev connectingr means when in` a conducting condition.

2. In a servo system, flne'and coarse transmission systems, a servomotor connected for control by the voltage outputs of saidfflne and coarsesystems, and acircuitfor mixing the fine and coarse error voltage outputs of :said systems, said circuit comprising an electron tube having a controly electrode, a pair of inputs adapted to be connected to two sources of voltage to be mixed,l means including a relatively high impedance for con-y necting one of said inputs to said control electrode,- means including a diode electron tube and a source of bias potential connected therewith, said tube being connected with the other input for blocking the voltage supplied thereto below a predetermined value but passing voltages in excess thereof to its output, and means for connecting the output of said last-mentioned means to said control electrode between it and said high impedance.

3. In a servo system, fine and coarse transmission systems, a servomotor connected for control by the voltage outputs of said ne and coarse systems, and a circuit for mixing the line and coarse error voltage outputs of said systems, said circuit comprising an electron tube having a control electrode, a pair of inputs adapted to be connected to two sources of voltage to be mixed, means including a relatively high impedance for connecting one of said inputs to said control electrode, means including a pair of diode electron tubes having space discharge paths connected for full phase operation of said applied voltage for blocking the voltage supplied thereto below a predetermined value but passing voltages in excess thereof to its output, a source of bias potential connected to both of said ydiode electron tubes, and means for connecting the output of said lastmentioned means to said control electrode between it and said high impedance, the impedance offered by said pairs of diodes being innite under blocking condition but low as compared to ,A filter |42. and-ia: D. C..,power` output stage |43 areal'so; provided,the D. (Lamthe value ofv said impedance connecting means when in a conducting condition.

4. In a servo system ne and coarse transmission systems, a servomotor connected for control by the voltage outputs of said fine and coarse systems, and a circuit for mixing the ne and coarse error voltage outputs of said systems, said circuit comprising an electron tube having a control electrode, a pair of inputs adapted to be connected to two sources of voltage to be mixed, means including a. relatively high impedance for connecting one of said inputs to said control electrode, means including a pair of diode electron tubes having a fixed bias for blocking the voltage supplied thereto below a predetermined value, but passing voltages in excess thereof to its output, and means for connecting the output of said lastmentioned means to said control electrode between it and said high impedance, the impedance of said pair of diodes being infinite when in blocking condition but low as compared to the impedance of said impedance connecting means when in a conducting condition.

5. In a system for mixing ne and coarse signal voltages and having an electrical circuit including an electron tube with a control electrode and two inputs adapted to be connected to two sources of voltage to be mixed, and means including relatively high impedance for connecting one of said inputs to said control electrode; the

combination therewith of means connected with the other input for blocking the voltage supply thereto below a predetermined value but passing voltages in excess thereof to its output, the output being connected to said control electrode, said blocking means comprising a pair of diodes connected in series relationship, one output line connected at a point joining said diodes, a condenser across both of said diodes, a pair of biasing voltage sources connected to bias said diodes in a non-conducting direction, a pair of balancing resistors in series with each of said biasing sources, and a Second output line connected at a point interconnecting said biasing voltages.

6. In a system for mixing fine and coarse signal voltages and having an electrical circuit including an electron tube with a control electrode and two inputs adapted to be connected to two sources of voltage to be mixed, and means including relatively high impedance for connecting one of said inputs to said control electrode; the combination therewith of means connected with the other input for blocking the voltage supply thereto below a predetermined value but passing voltages in excess thereof to its output, the output being connected to said control electrode; said blocking means comprising a pair of diodes connected in series relationship, one output line connected to a point joining said diodes, a pair of voltage sources connected to bias said diodes, and a resistance-capacitance network connecting said diodes with said biasing source to provide thereby full phase operation of said blocking circuit.

'7. In a system for mixing two voltages, amplifying means adapted to be connected to the two sources of voltage to be mixed, means including a relatively high impedance for connecting said amplifying means with a iirst of said two voltages, means comprising a diode electron tube and a source of bias potential connected therewith, said tube being connected with the second of said two voltages and being operable to block the current supplied thereto below a predetermined value but to pass a current in excess thereof to its output, and means for connecting the output of said last-mentioned means to said amplifying means between it and said high impedance.

' RAYMOND C. GOERTZ.

REFERENCES CITED The ioliowing references are of record in the iile of this patent:

UNITED STATES PATENTS Number Name Date 2,324,809 Edwards July 29, 1944 2,409,970 Agins Oct. 22, 1946 2,414,384 Moseley Jan. 14, 1947 2,455,364 Hays Jr Dec. 7, 1948 

